The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having a multi-layer structure.
A prior multi-layer semiconductor device, e.g., having a two-layered interconnection structure is shown in FIG. 1. As shown, a first interconnection layer 3 (conductive layer) is formed on a semiconductor substrate 1 with an insulating film 2 interposed therebetween. An interlaying insulating film 4 is formed over the entire upper surface of the first interconnection layer 3. Then, the insulating film 4 is masked and etched at a predetermined location thereof to form a first contact hole 5. Metal, for example, aluminum, is deposited over the entire upper surface of the insulating film 4 containing the first contact hole 5. The aluminum layer formed is patterned to form a second interconnection layer (conductive layer) 6. In the depositing process for forming the second interconnection layer 6, the aluminum penetrates into the first contact hole 5 to stick to the exposed portion of the first interconnection layer 3 and to the inner side wall of the insulating film 4, thereby interconnecting the first interconnection layer 3 and the second interconnection layer 6.
According to the prior manufacturing method, however, while the aluminum is being deposited to form the second interconnection layer 6, some aluminum hangs over the upper peripheral edge of the first contact hole 5, as shown in FIG. 2. The overhanging aluminum hinders aluminum deposition on the inner side wall of the first contact hole 5, preventing the formation of aluminum film there or permitting only a very thin aluminum film to be formed. Therefore, the second interconnection layer 6 tends to disconnect from the inner side wall of the first contact hole 5. Even if the second interconnection layer 6 is not disconnected, the semiconductor device tends to be destroyed during the course of operation. The reason for this is that the thin aluminum deposited layer on the inner side wall of the first contact hole 5 has a high current density when the device is operated, and the large amount of Joule heat generated destroys the thin film. In this respect, the prior semiconductor device involves a problem in reliability.
Another prior art of the multi-layer semiconductor device having three-layers is illustrated in FIG. 3. As shown, the first interconnection layer 3 is layered on the insulating film 2 formed on the substrate 1. The insulating film 4 is then formed on the first interconnection layer 3 and is maksed and etched at a proper location to form the first contact hole 5. Then, the second interconnection layer 6 is formed on the insulating film 4, connecting with the first interconnection layer 3 through the first contact hole 5. Then, an insulating layer 7 is formed over the entire upper surface of the second interconnection layer 6. In the next step, a second contact hole 8, which is larger than the first contact hole 5, is formed in the insulating layer 7 at the location just above the first contact hole 5 of the insulating film 4. Aluminum is deposited over the entire upper surface of the insulating layer 7 including the second contact hole 8. In turn, the aluminum film is patterned to form a third interconnection layer 9 interconnecting with the second interconnection layer 6.
High intergration density is one of the most important requirements in the fabrication of the integrated circuits. Therefore, it is desirable that the holes 5 and 8 be as small as possible. In this respect, as in the prior art case, it is necessary that the diameter of the second contact hole 8 be at least equal to that of the first contact hole 5.
To form the second contact hole 8, the following process steps are taken. A photoresist film is first formed on the insulating layer 7. Then, a mask with a predetermined pattern is applied onto the photoresist film. The insulating layer 7 having the mask-layered photoresist film is exposed to light. Finally, a portion of the insulating layer 7 where the second contact hole 8 is to be formed is etched away to form the same hole 8. In the exposing step in the above fabricating process, light irregularly reflects on the second interconnection layer 6, making the diameters of the holes 5 and 8 unequal to each other. Further, it is required that the hole formed in the photoresist has a large enough diameter to prevent irregular reflection. Therefore, the diameter of the second contact hole 8 formed is necessarily larger than the first contact hole 5.